Food products have long been manufactured by the use of extrusion. Examples can be found regularly through the prior art. Normally a rice or other cereal-based pre-mix is passed through either a single or twin screw extruder. At the time of passing through the extruding head the food product tends to suffer a great loss of flavour as these are normally relatively highly volatile substances. Due to the heat of extrusion and sudden pressure change they can quickly evaporate or flash off. Colouring agents quite often lose effectiveness due to heat degradation as they are quite often heat sensitive. It has therefore been standard practice to subsequently coat the extrudant with colouring and/or flavouring additives, and for further processing to take place. This normally results in the completed food product having a high concentration of colouring additives on the surface which can be picked-up by a consumer of the food product. This pick-up, usually on the fingers, is disliked by many consumers and is particularly relevant in the area of snack foods. Furthermore, particularly when coating is applied by a spray, a relatively high fat content is used to suspend the flavour and colour components as a slurry and obtain a relatively even coating on the extrudant. Snack foods produced by these processes generally have a fat content ranging from 18% to as high as 41%, by weight. These high fat snack foods have calorie contents ranging from 450 up to 575 calories per 100 grams. To consider for example U.S. Pat. No. 4,225,630 to Pitchon, there is described and illustrated a process for the manufacture of a food product by extrusion. However, with this particular food product fat is deliberately added into the extruder in the metering zone, which is the zone or stage directly before the extrusion die. By doing this the fat can be intimately mixed with the material as it is extruded and does not interfere with the expansion or cohesiveness of the product to a significant degree.
U.S. Pat. No. 4,759,939 to Keller & Vowles is directed to a process for producing pretzels. With the process, a dry mixture of flour, corn syrup, solids and salt is introduced into the extruder, and water is added when passing along the extruder. The resultant mixture is extruded at a non-cooking temperature so that a self-suporting ribbon can pass through a region where it is sprayed with a caustic solution. It is subsequently baked. The principal object of the invention is to control the moisture content so that the time taken in the baking oven is reduced. For that reason, the initial mix is substantially dry, and thus the addition of water can be carefully controlled during the extrusion.
International Application PCT/U.S.86/01081(W86/06938) of Nabisco is directed to a continuous process for mixing, cooking and extruding a bran cereal composition in a unitary-extruder. Dry ingredients are mixed and then passed into the twin-screw extruder where they are mixed with a syrup, which includes at least one sugar. The resultant wet mixture is cooked in a cooking zone in the extruder to form a cooked bran mixture, which is then passed through the die to extrude the resultant product. The resultant extrudant pieces fall onto a moving belt and are subsequently dried and toasted. Low pressure is used to avoid plasticisation of the extruded product. There is no colour or flavour added.
In their GB patent application 2186176A, Vincent Process Limited describe a method of manufacturing a food product by extrusion wherein the material is introduced into the extruder and is cooked within the extruder. Water or any other fluid solution is added at high pressure into the extruder immediately before the die head. This is to reduce the temperature of the cooked mass and to arrest expansion as the material leaves the die head. Flavourings and/or colourings can be introduced at the same time, again under high pressure. As the flavour bodies are introduced at that time, the temperature of the mass has been reduced and therefore the flavour bodies are not subjected to the high temperature and pressure cooking process.
A German patent 4,112,861 to Humboldt University describes a process for extruding a food product where whole-grains are fed into an extruder. In passing along the extruder, the grains are ground and at that area of the extruder where the grains have been ground, there is injected a solution, which is acidic, basic, or an electrolyte. The injection is through the wall of the extruder so as to control the pH of the product. The pH value is is adjusted by varying the amount of the acid, base or electrolyte injected. As the product has already been partially ground within the extruder, the contact surface area is increased significantly. However, as the whole-grains are effectively ground during the extrusion process, it is not necessary to pre-grind the grains. The pH of the extruded product is measured so that feedback can be used to control the amount of acid, base or electrolyte added. In this way the browning and formation of flavourings during processing can be controlled more accurately.
USSR patent 867350 relates to equipment for thermo-mechanical processing of starch-containing raw materials. This includes a screw extruder having an injection nozzle for injecting water or like reagent into the relatively dry mass being passed along the screw extruder. A projection on the shaft of the extruder cleans the injector nozzles.
In their article "Volatiles Retention as Influenced by Method of Addition During Extrusion Cooking" as published in Journal of Food Science, Vol. 61 No. 5, 1996 at page 985, Collengode, Hanna & Cupert consider the volatile component retention of a corn-starch based food product passing along an extruder. It was found that volatile component retention was enhanced when they were injected into the metering zone of the extruder barrel as compared to pre-mixing with the feed. A twin-screw extruder was used.
It is therefore one object of the present invention to provide a method of manufacturing food products where flavour and/or colouring compounds are added to the initial mix prior to being fed into a screw extruder, be it a twin-screw or single-screw extruder, and further flavouring and/or colouring compounds are added at an apropriate stage during the extrusion process so that the food products, when extruded, are in a "ready to eat" condition.
Another object to is to provide a food product produced by the method.
It is the further object of the present invention that the addition of the colourings and/or flavourings is such that a reduced fat, or even a low fat, food product can result. For another object of the invention to produce foods which have calorie contents ranging from 420 calories per 100 grams down to as low as 380 calories per 100 grams.